Three-piece infrared single wavelength projection lens system

ABSTRACT

A three-piece infrared single wavelength projection lens system includes, in order from an image side to an image source side: a first lens element with a positive refractive power; a second lens element with a negative refractive power; a third lens element with a positive refractive power; and a stop disposed before an image source-side surface of the first lens element or between an image-side surface of the first lens element and an image source-side surface of the second lens element. Such arrangements can provide a three-piece infrared single wavelength projection lens system with better image sensing function.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a projection lens system, and moreparticularly to a miniaturized three-piece infrared single wavelengthprojection lens system applicable to electronic products.

Description of the Prior Art

Nowadays digital imaging technology is constantly innovating andchanging, in particular, digital carriers, such as, digital camera andmobile phone and so on, have become smaller in size, so CCD (ChargeCoupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensoris also required to be more compact. In addition to be used in the fieldof photography, in recent years, infrared focusing lens has also be usedin infrared receiving and sensing field of the game machine, and inorder to make the scope of game machine induction user more broader,wide-angle lens group has become the mainstream for receiving infraredwavelength at present.

The applicant has also put forward a number of lens groups related toinfrared wavelength reception, however, at present, the game machine isbased on a more three-dimensional, real and immediate 3D game, thecurrent or the applicant's previous lens groups are all 2D plane games,which cannot meet the 3D game focusing on the deep induction efficacy.

Special infrared receiving and induction lens groups for game machinesare made of plastic for the pursuit of low cost, however, poor materialtransparency is one of the key factors that affect the depth detectionaccuracy of the game machine, and plastic lenses are easy to overheat ortoo cold in ambient temperature, so that the focal length of the lensgroup will be changed and cannot focus accurately. Therefore, thecurrent infrared receiving and induction lens groups cannot meet the 3Dgame depth precise induction requirement.

The present invention mitigates and/or obviates the aforementioneddisadvantages.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to provide athree-piece infrared single wavelength projection lens system withbetter image sensing function.

Therefore, a three-piece infrared single wavelength projection lenssystem in accordance with the present invention comprises, in order froman image side to an image source side: a first lens element with apositive refractive power having an image-side surface being convex nearan optical axis, at least one of the image-side surface and an imagesource-side surface of the first lens element being aspheric; a secondlens element with a negative refractive power having an imagesource-side surface being concave near the optical axis, at least one ofan image-side surface and the image source-side surface of the secondlens element being aspheric; a third lens element with a positiverefractive power having an image-side surface being concave near anoptical axis and an image source-side surface being convex near theoptical axis, at least one of the image-side surface and the imagesource-side surface of the third lens element being aspheric; a stopdisposed before the image source-side surface of the first lens elementor between the image-side surface of the first lens element and theimage source-side surface of the second lens element.

Preferably, a focal length of the three-piece infrared single wavelengthprojection lens system is f, a focal length of the first lens elementand the second lens element combined is f12, and they satisfy therelation: 0.6<f/f12<1.6. Therefore, appropriate refractive powers of thefirst and second lens elements can obtain a wide field of view andmaintain the objective of miniaturization of the system.

Preferably, the focal length of the three-piece infrared singlewavelength projection lens system is f, a focal length of the secondlens element and the third lens element combined is f23, and theysatisfy the relation: 0.1<f/f23<1.3, so that the shortening of the totallength of the system and the correction of aberration can be balanced.

Preferably, a focal length of the first lens element is f1, a focallength of the second lens element is f2, and they satisfy the relation:−3.0<f1/f2<−1.7, so that the refractive power of the first lens elementand the second lens element are more suitable, it will be favorable toavoid the excessive increase of aberration of the system.

Preferably, the focal length of the second lens element is f2, a focallength of the third lens element is f3, and they satisfy the relation:−0.55<f2/f3<−0.15, so that the refractive power of the second lenselement and the third lens element are more balanced, it will befavorable to correct the aberration of the system and reduce thesensitivity of the system.

Preferably, the focal length of the first lens element is f1, the focallength of the third lens element is f3, and they satisfy the relation:0.5<f1/f3<1.3, so that the refractive power of the first lens elementcan be distributed effectively, so as to reduce the sensitivity of thethree-piece infrared single wavelength projection lens system.

Preferably, the focal length of the first lens element is f1, the focallength of the second lens element and the third lens element combined isf23, and they satisfy the relation: 0.02<f1/f23<0.46, so that theresolution can be improved evidently.

Preferably, the focal length of the first lens element and the secondlens element combined is f12, the focal length of the third lens elementis f3, and they satisfy the relation: 1.34<f12/f3<4.05, so that theresolution can be improved evidently.

Preferably, a radius of curvature of the image-side surface of the firstlens element is R1, a radius of curvature of the image source-sidesurface of the first lens element is R2, and they satisfy the relation:−3.38<R1/R2<0.45, which can reduce the spherical aberration andastigmatism of the three-piece infrared single wavelength projectionlens system.

Preferably, a radius of curvature of the image-side surface of thesecond lens element is R3, a radius of curvature of the imagesource-side surface of the second lens element is R4, and they satisfythe relation: −1.87<R3/R4<6.23, which can reduce the sphericalaberration and astigmatism of the three-piece infrared single wavelengthprojection lens system.

Preferably, a radius of curvature of the image-side surface of the thirdlens element is R5, a radius of curvature of the image source-sidesurface of the third lens element is R6, and they satisfy the relation:0.5<R5/R6<3.2, which can reduce the spherical aberration and astigmatismof the three-piece infrared single wavelength projection lens system.

Preferably, a central thickness of the first lens element along theoptical axis is CT1, a central thickness of the second lens elementalong the optical axis is CT2, and they satisfy the relation:0.8<CT1/CT2<3.5, which is favorable to the formation and homogeneity oflenses.

Preferably, the central thickness of the second lens element along theoptical axis is CT2, a central thickness of the third lens element alongthe optical axis is CT3, and they satisfy the relation: 0.1<CT2/CT3<1.6,so that the image quality and the sensitivity of the system can bebalanced properly.

Preferably, the central thickness of the first lens element along theoptical axis is CT1, the central thickness of the third lens elementalong the optical axis is CT3, and they satisfy the relation:0.1<CT1/CT3<1.1, which is favorable to the formation and homogeneity oflenses.

Preferably, the focal length of the three-piece infrared singlewavelength projection lens system is f, a distance from the image-sidesurface of the first lens element to the image plane along the opticalaxis is TL, and they satisfy the relation: 1.0<f/TL<2.0, it will befavorable to maintain the objective of miniaturization of thethree-piece infrared single wavelength projection lens system, which canbe used in thin electronic products.

Preferably, a refractive index of the first lens element is n1, arefractive index of the second lens element is n2, a refractive index ofthe third lens element is n3, and they satisfy the relations: n1>1.6,n2>1.6 and n3>1.6, it will be favorable to match and reconcile the lenselements of the three-piece infrared single wavelength projection lenssystem, so as to provide better aberration balance ability.

The present invention will be presented in further details from thefollowing descriptions with the accompanying drawings, which show, forpurpose of illustrations only, the preferred embodiments in accordancewith the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a three-piece infrared single wavelength projection lenssystem in accordance with a first embodiment of the present invention;

FIG. 1B shows the astigmatic field curve and the distortion curve of thefirst embodiment of the present invention;

FIG. 2A shows a three-piece infrared single wavelength projection lenssystem in accordance with a second embodiment of the present invention;

FIG. 2B shows the astigmatic field curve and the distortion curve of thesecond embodiment of the present invention;

FIG. 3A shows a three-piece infrared single wavelength projection lenssystem in accordance with a third embodiment of the present invention;

FIG. 3B shows the astigmatic field curve and the distortion curve of thethird embodiment of the present invention;

FIG. 4A shows a three-piece infrared single wavelength projection lenssystem in accordance with a fourth embodiment of the present invention;

FIG. 4B shows the astigmatic field curve and the distortion curve of thefourth embodiment of the present invention;

FIG. 5A shows a three-piece infrared single wavelength projection lenssystem in accordance with a fifth embodiment of the present invention;and

FIG. 5B shows the astigmatic field curve and the distortion curve of thefifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1A and 1B, FIG. 1A shows a three-piece infraredsingle wavelength projection lens system in accordance with a firstembodiment of the present invention, and FIG. 1B shows, in order fromleft to right, the astigmatic field curve and the distortion curve ofthe first embodiment of the present invention. A three-piece infraredsingle wavelength projection lens system in accordance with the firstembodiment of the present invention comprises a stop 100 and a lensgroup. The lens group comprises, in order from an image side to an imagesource side: a first lens element 110, a second lens element 120, athird lens element 130, and an image source plane 180, wherein thethree-piece infrared single wavelength projection lens system has atotal of three lens elements with refractive power. The stop 100 isdisposed between an image-side surface 111 of the first lens element 110and an image-side surface 121 of the second lens element 120.

The first lens element 110 with a positive refractive power has theimage-side surface 111 being convex near an optical axis 190 and animage source-side surface 112 being convex near the optical axis 190,the image-side surface 111 and the image source-side surface 112 areaspheric, and the first lens element 110 is made of plastic material.

The second lens element 120 with a negative refractive power has theimage-side surface 121 being convex near the optical axis 190 and animage source-side surface 122 being concave near the optical axis 190,the image-side surface 121 and the image source-side surface 122 areaspheric, and the second lens element 120 is made of plastic material.

The third lens element 130 with a positive refractive power has animage-side surface 131 being concave near the optical axis 190 and animage source-side surface 132 being convex near the optical axis 190,the image-side surface 131 and the image source-side surface 132 areaspheric, and the third lens element 130 is made of plastic material.

The equation for the aspheric surface profiles of the respective lenselements of the first embodiment is expressed as follows:

$z = {\frac{{ch}^{2}}{1 + \left\lbrack {1 - {\left( {k + 1} \right)c^{2}h^{2}}} \right\rbrack^{0.5}} + {A\; h^{4}} + {Bh}^{6} + {Ch}^{8} + {Dh}^{10} + {Eh}^{12} + {Gh}^{14} + \ldots}$

wherein:

z represents the value of a reference position with respect to a vertexof the surface of a lens and a position with a height h along theoptical axis 190;

c represents a paraxial curvature equal to 1/R (R: a paraxial radius ofcurvature);

h represents a vertical distance from the point on the curve of theaspheric surface to the optical axis 190;

k represents the conic constant;

A

B

C

D

E

G

. . . : represent the high-order aspheric coefficients.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, a focal length of the three-pieceinfrared single wavelength projection lens system is f, a f-number ofthe three-piece infrared single wavelength projection lens system isFno, the three-piece infrared single wavelength projection lens systemhas a maximum view angle (field of view) FOV, and they satisfy therelations: f=5.97 mm; Fno=2.6; and FOV=4.89 degrees.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, the focal length of the three-pieceinfrared single wavelength projection lens system is f, a focal lengthof the first lens element 110 and the second lens element 120 combinedis f12, and they satisfy the relation: f/f12=1.429.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, the focal length of the three-pieceinfrared single wavelength projection lens system is f, a focal lengthof the second lens element 120 and the third lens element 130 combinedis f23, and they satisfy the relation: f/f23=0.512.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, a focal length of the first lenselement 110 is f1, a focal length of the second lens element 120 is f2,and they satisfy the relation: f1/f2=−2.088.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, the focal length of the second lenselement 120 is f2, a focal length of the third lens element 130 is f3,and they satisfy the relation: f2/f3=−0.383.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, the focal length of the first lenselement 110 is f1, the focal length of the third lens element 130 is f3,and they satisfy the relation: f1/f3=0.8.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, the focal length of the first lenselement 110 is f1, the focal length of the second lens element 120 andthe third lens element 130 combined is f23, and they satisfy therelation: f1/f23=0.175.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, the focal length of the first lenselement 110 and the second lens element 120 combined is f12, the focallength of the third lens element 130 is f3, and they satisfy therelation: f12/f3=1.637.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, a radius of curvature of theimage-side surface 111 of the first lens element 110 is R1, a radius ofcurvature of the image source-side surface 112 of the first lens element110 is R2, and they satisfy the relation: R1/R2=−3.076.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, a radius of curvature of theimage-side surface 121 of the second lens element 120 is R3, a radius ofcurvature of the image source-side surface 122 of the second lenselement 120 is R4, and they satisfy the relation: R3/R4=3.559.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, a radius of curvature of theimage-side surface 131 of the third lens element 130 is R5, a radius ofcurvature of the image source-side surface 132 of the third lens element130 is R4, and they satisfy the relation: R5/R6=0.75.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, a central thickness of the first lenselement 110 along the optical axis 190 is CT1, a central thickness ofthe second lens element 120 along the optical axis 190 is CT2, and theysatisfy the relation: CT1/CT2=1.004.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, the central thickness of the secondlens element 120 along the optical axis 190 is CT2, a central thicknessof the third lens element 130 along the optical axis 190 is CT3, andthey satisfy the relation: CT2/CT3=1.354.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, the central thickness of the firstlens element 110 along the optical axis 190 is CT1, the centralthickness of the third lens element 130 along the optical axis 190 isCT3, and they satisfy the relation: CT1/CT3=1.360.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, the focal length of the three-pieceinfrared single wavelength projection lens system is f, a distance fromthe object-side surface 111 of the first lens element 110 to the imageplane 180 along the optical axis 190 is TL, and they satisfy therelation: f/TL=1.637.

In the first embodiment of the present three-piece infrared singlewavelength projection lens system, a refractive index of the first lenselement 110 is n1, a refractive index of the second lens element 120 isn2, a refractive index of the third lens element 130 is n3, and theysatisfy the relations: n1=1.65, n2=1.65 and n3=1.65.

The detailed optical data of the first embodiment is shown in table 1,and the aspheric surface data is shown in table 2.

TABLE 1 Embodiment 1 f(focal length) = 5.97 mm, Fno = 2.6, FOV = 4.89deg. surface Curvature Radius Thickness Material Index Abbe # Focallength 0 object infinity 700 1 infinity 0 2 Lens 1 4.978 (ASP) 0.724plastic 1.65 21.5 2.044 3 −1.619 (ASP) −0.224 4 stop infinity 0.250 5Lens 2 0.687 (ASP) 0.720 plastic 1.65 21.5 −0.979 6 0.193 (ASP) 1.012 7Lens 3 −0.334 (ASP) 0.532 plastic 1.65 21.5 2.555 8 −0.445 (ASP) 0.499 9Image infinity — source plane

TABLE 2 Aspheric Coefficients surface 2 3 5 K: −6.9507E+01 −6.5824E+00−4.9731E−01 A: 2.6183E−01 9.3099E−02 −1.6216E−01 B: −2.6153E−01−1.9801E−01 −5.5685E−01 C: 9.7126E−02 1.0107E−01 −1.7392E+00 D:−1.2788E−02 5.6492E−02 6.3501E+00 E: 1.5759E−03 −8.1979E−02 −6.4523E+00F: 2.3038E−03 2.9121E−02 2.2633E+00 surface 6 7 8 K: −8.0491E−01−5.5390E−01 −1.5357E+00 A: −4.8088E+00 6.3540E−01 −3.1526E+00 B:−8.4992E+00 −5.0180E+02 4.7309E+01 C: −1.4301E+02 2.6285E+04 −7.5592E+02D: 2.1212E+03 −7.0107E+05 6.0844E+03 E: −1.3929E+04 8.7304E+06−2.4555E+04 F: 3.7563E+04 −4.1319E+07 3.9097E+04

The units of the radius of curvature, the thickness and the focal lengthin table 1 are expressed in mm, the surface numbers 0-9 represent thesurfaces sequentially arranged from the image-side to the imagesource-side along the optical axis. In table 2, k represents the coniccoefficient of the equation of the aspheric surface profiles, and A

B

C

D

E

F

. . . : represent the high-order aspheric coefficients. The tablespresented below for each embodiment are the corresponding schematicparameter, aberration curves, and the definitions of the tables are thesame as Table 1 and Table 2 of the first embodiment. Therefore, anexplanation in this regard will not be provided again.

Referring to FIGS. 2A and 2B, FIG. 2A shows a three-piece infraredsingle wavelength projection lens system in accordance with a secondembodiment of the present invention, and FIG. 2B shows, in order fromleft to right, the astigmatic field curve and the distortion curve ofthe second embodiment of the present invention. A three-piece infraredsingle wavelength projection lens system in accordance with the secondembodiment of the present invention comprises a stop 200 and a lensgroup. The lens group comprises, in order from an image side to an imagesource side: a first lens element 210, a second lens element 220, athird lens element 230, and an image source plane 280, wherein thethree-piece infrared single wavelength projection lens system has atotal of three lens elements with refractive power. The stop 200 isdisposed between an image source-side surface 212 of the first lenselement 210 and an image-side surface 221 of the second lens element220.

The first lens element 210 with a positive refractive power has animage-side surface 211 being convex near an optical axis 290 and theimage source-side surface 212 being convex near the optical axis 290,the image-side surface 211 and the image source-side surface 212 areaspheric, and the first lens element 210 is made of plastic material.

The second lens element 220 with a negative refractive power has theimage-side surface 221 being convex near the optical axis 290 and animage source-side surface 222 being concave near the optical axis 290,the image-side surface 221 and the image source-side surface 222 areaspheric, and the second lens element 220 is made of plastic material.

The third lens element 230 with a positive refractive power has animage-side surface 231 being concave near the optical axis 290 and animage source-side surface 232 being convex near the optical axis 290,the image-side surface 231 and the image source-side surface 232 areaspheric, and the third lens element 230 is made of plastic material.

The detailed optical data of the second embodiment is shown in table 3,and the aspheric surface data is shown in table 4.

TABLE 3 Embodiment 2 f(focal length) = 5.60 mm, Fno = 2.9, FOV = 10.67deg. surface Curvature Radius Thickness Material Index Abbe # Focallength 0 object infinity 700 1 infinity 0 2 Lens 1 1.064 (ASP) 0.768plastic 1.65 21.5 1.623 3 −15.065 (ASP) 0.014 4 stop infinity 0.549 5Lens 2 1.704 (ASP) 0.236 plastic 1.65 21.5 −0.592 6 0.287 (ASP) 0.757 7Lens 3 −0.999 (ASP) 0.65 plastic 1.65 21.5 1.997 8 −0.694 (ASP) 0.543 9Image infinity — source plane

TABLE 4 Aspheric Coefficients surface 2 3 5 K: −1.6241E−01 −5.4705E+029.2656E−01 A: −2.9461E−02 −2.2284E−02 −2.3385E+00 B: 2.2146E−024.1664E−01 7.4193E+00 C: −1.8500E−04 −1.8224E+00 −3.7376E+00 D:−2.6263E−01 3.9034E+00 −1.4259E+02 E: 4.5051E−01 −4.0999E+00 9.5449E+02F: −2.5746E−01 1.6431E+00 −2.1616E+03 surface 6 7 8 K: −6.2380E−01−1.1766E+02 −1.4405E+00 A: −3.4702E+00 −9.9908E−01 −8.4013E−01 B:6.9321E+00 6.2334E+01 2.7131E+00 C: 4.9255E+02 −4.3705E+02 −2.1645E+01D: −1.2643E+04 1.3293E+03 8.1906E+01 E: 1.5252E+05 −7.8347E+02−1.6494E+02 F: −6.5218E+05 −1.7926E+03 1.3327E+02

In the second embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the second embodiment, so an explanationin this regard will not be provided again.

Moreover, these parameters can be calculated from Table 3 and Table 4 asthe following values and satisfy the following conditions:

Embodiment 2 f [mm] 5.60 f12/f3 2.839 Fno 2.9 f/TL 1.589 FOV [deg.]10.67 R1/R2 −0.071 f/f12 0.987 R3/R4 5.935 f/f23 0.208 R5/R6 1.440 f1/f2−2.743 CT1/CT2 3.248 f2/f3 −0.296 CT2/CT3 0.361 f1/f3 0.813 CT1/CT31.174 f1/f23 0.060

Referring to FIGS. 3A and 3B, FIG. 3A shows a three-piece infraredsingle wavelength projection lens system in accordance with a thirdembodiment of the present invention, and FIG. 3B shows, in order fromleft to right, the astigmatic field curve and the distortion curve ofthe third embodiment of the present invention. A three-piece infraredsingle wavelength projection lens system in accordance with the thirdembodiment of the present invention comprises a stop 300 and a lensgroup. The lens group comprises, in order from an image side to an imagesource side: a first lens element 310, a second lens element 320, athird lens element 330, and an image source plane 380, wherein thethree-piece infrared single wavelength projection lens system has atotal of three lens elements with refractive power. The stop 300 isdisposed between an image-side surface 311 and an image source-sidesurface 312 of the first lens element 310.

The first lens element 310 with a positive refractive power has theimage-side surface 311 being convex near an optical axis 390 and theimage source-side surface 312 being convex near the optical axis 390,the image-side surface 311 and the image source-side surface 312 areaspheric, and the first lens element 310 is made of plastic material.

The second lens element 320 with a negative refractive power has animage-side surface 321 being concave near the optical axis 390 and animage source-side surface 322 being concave near the optical axis 390,the image-side surface 321 and the image source-side surface 322 areaspheric, and the second lens element 320 is made of plastic material.

The third lens element 330 with a positive refractive power has animage-side surface 331 being concave near the optical axis 390 and animage source-side surface 332 being convex near the optical axis 390,the image-side surface 331 and the image source-side surface 332 areaspheric, and the third lens element 330 is made of plastic material.

The detailed optical data of the third embodiment is shown in table 5,and the aspheric surface data is shown in table 6.

TABLE 5 Embodiment 3 f(focal length) = 5.00 mm, Fno = 2.8, FOV = 11.53deg. surface Curvature Radius Thickness Material Index Abbe # Focallength 0 object infinity 700 1 infinity 0.479 2 stop infinity −0.479 3Lens 1 0.960 (ASP) 0.793 plastic 1.636 24 1.558 4 −100.005 (ASP) 0.573 5Lens 2 −0.833 (ASP) 0.250 plastic 1.636 24 −0.570 6 0.669 (ASP) 0.524 7Lens 3 −1.706 (ASP) 0.818 plastic 1.636 24 1.691 8 −0.762 (ASP) 0.545 9Image infinity — source plane

TABLE 6 Aspheric Coefficients surface 3 4 5 K: −2.6398E−01 5.0000E+02−2.8996E+01 A: 4.1118E−04 1.4575E−01 −1.1315E+00 B: 8.5137E−022.9778E−01 6.7305E+00 C: 1.0540E−03 −1.8603E+00 −2.8827E+01 D:−3.1305E−01 4.0358E+00 −2.6092E+02 E: 5.3893E−01 −4.0708E+00 2.3782E+03F: −2.5746E−01 1.6431E+00 −2.1616E+03 G 1.5880E−02 −1.7845E−01−1.6700E+04 surface 6 7 8 K: 2.1367E+00 −1.2598E+02 −7.6695E−01 A:4.8124E+00 −3.5237E+00 −6.7446E−01 B: −5.8232E+01 3.8053E+01 3.9725E+00C: 8.3806E+02 −2.8782E+02 −2.1423E+01 D: −1.4158E+04 1.0334E+036.5252E+01 E: 1.5056E+05 −1.1587E+03 −1.2469E+02 F: −6.5218E+05−1.7926E+03 1.3327E+02 G 3.4570E+05 4.0438E+03 −6.0733E+01

In the third embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the third embodiment, so an explanation inthis regard will not be provided again.

Moreover, these parameters can be calculated from Table 5 and Table 6 asthe following values and satisfy the following conditions:

Embodiment 3 f [mm] 5.00 f12/f3 3.392 Fno 2.8 f/TL 1.427 FOV [deg.]11.53 R1/R2 −0.010 f/f12 0.871 R3/R4 −1.246 f/f23 0.814 R5/R6 2.240f1/f2 −2.735 CT1/CT2 3.177 f2/f3 −0.337 CT2/CT3 0.305 f1/f3 0.921CT1/CT3 0.970 f1/f23 0.254

Referring to FIGS. 4A and 4B, FIG. 4A shows a three-piece infraredsingle wavelength projection lens system in accordance with a fourthembodiment of the present invention, and FIG. 4B shows, in order fromleft to right, the astigmatic field curve and the distortion curve ofthe fourth embodiment of the present invention. A three-piece infraredsingle wavelength projection lens system in accordance with the fourthembodiment of the present invention comprises a stop 400 and a lensgroup. The lens group comprises, in order from an image side to an imagesource side: a first lens element 410, a second lens element 420, athird lens element 430, and an image source plane 480, wherein thethree-piece infrared single wavelength projection lens system has atotal of three lens elements with refractive power. The stop 400 isdisposed between an image-side surface 411 and an image source-sidesurface 412 of the first lens element 410.

The first lens element 410 with a positive refractive power has theimage-side surface 411 being convex near an optical axis 490 and theimage source-side surface 412 being concave near the optical axis 490,the image-side surface 411 and the image source-side surface 412 areaspheric, and the first lens element 410 is made of plastic material.

The second lens element 420 with a negative refractive power has animage-side surface 421 being concave near the optical axis 490 and animage source-side surface 422 being concave near the optical axis 490,the image-side surface 421 and the image source-side surface 422 areaspheric, and the second lens element 420 is made of plastic material.

The third lens element 430 with a positive refractive power has animage-side surface 431 being concave near the optical axis 490 and animage source-side surface 432 being convex near the optical axis 490,the image-side surface 431 and the image source-side surface 432 areaspheric, and the third lens element 430 is made of plastic material.

The detailed optical data of the fourth embodiment is shown in table 7,and the aspheric surface data is shown in table 8.

TABLE 7 Embodiment 4 f(focal length) = 4.80 mm, Fno = 2.8, FOV = 11.99deg. surface Curvature Radius Thickness Material Index Abbe # Focallength 0 object infinity 700 1 infinity 0.479 2 stop infinity −0.479 3Lens 1 0.921 (ASP) 0.740 plastic 1.636 24 1.670 4 6.376 (ASP) 0.610 5Lens 2 −0.990 (ASP) 0.250 plastic 1.636 24 −0.650 6 0.730 (ASP) 0.606 7Lens 3 −2.318 (ASP) 0.754 plastic 1.636 24 1.653 8 −0.792 (ASP) 0.544 9Image infinity — source plane

TABLE 8 Aspheric Coefficients surface 3 4 5 K: −2.8762E−01 −1.4622E+02−2.8281E+01 A: 1.3589E−02 1.6193E−01 −2.7394E+00 B: 1.2126E−01−1.9416E−01 3.8785E+01 C: −7.3627E−01 2.3439E−01 −6.7499E+02 D:2.8705E+00 3.5854E−01 8.2993E+03 E: −5.9017E+00 −2.6531E+00 −6.4278E+04F: 6.3347E+00 4.3969E+00 2.7238E+05 G −2.7556E+00 −2.7840E+00−4.7500E+05 surface 6 7 8 K: 2.7667E+00 −1.7085E+02 −1.6623E+00 A:1.1642E+00 −1.5475E+00 −5.5562E−01 B: −4.2362E+00 1.4958E+01 2.1309E+00C: −2.6773E+02 −1.4428E+02 −1.2893E+01 D: 8.7323E+03 8.9714E+023.8135E+01 E: −1.3710E+05 −3.4259E+03 −6.0214E+01 F: 1.0155E+067.1886E+03 3.9800E+01 G −2.9300E+06 −6.1517E+03 −2.0552E+00

In the fourth embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the fourth embodiment, so an explanationin this regard will not be provided again.

Moreover, these parameters can be calculated from Table 7 and Table 8 asthe following values and satisfy the following conditions:

Embodiment 4 f [mm] 4.80 f12/f3 3.566 Fno 2.8 f/TL 1.370 FOV [deg.]11.99 R1/R2 0.144 f/f12 0.814 R3/R4 −1.356 f/f23 1.176 R5/R6 2.926 f1/f2−2.570 CT1/CT2 2.962 f2/f3 −0.393 CT2/CT3 0.331 f1/f3 1.010 CT1/CT30.981 f1/f23 0.409

Referring to FIGS. 5A and 5B, FIG. 5A shows a three-piece infraredsingle wavelength projection lens system in accordance with a fifthembodiment of the present invention, and FIG. 5B shows, in order fromleft to right, the astigmatic field curve and the distortion curve ofthe fifth embodiment of the present invention. A three-piece infraredsingle wavelength projection lens system in accordance with the fifthembodiment of the present invention comprises a stop 500 and a lensgroup. The lens group comprises, in order from an image side to an imagesource side: a first lens element 510, a second lens element 520, athird lens element 530, and an image source plane 580, wherein thethree-piece infrared single wavelength projection lens system has atotal of three lens elements with refractive power. The stop-500 isdisposed between an image-side surface 511 and an image source-sidesurface 512 of the first lens element 510.

The first lens element 510 with a positive refractive power has theimage-side surface 511 being convex near an optical axis 590 and theimage source-side surface 512 being concave near the optical axis 590,the image-side surface 511 and the image source-side surface 512 areaspheric, and the first lens element 510 is made of plastic material.

The second lens element 520 with a negative refractive power has animage-side surface 521 being concave near the optical axis 590 and animage source-side surface 522 being concave near the optical axis 590,the image-side surface 521 and the image source-side surface 522 areaspheric, and the second lens element 520 is made of plastic material.

The third lens element 530 with a positive refractive power has animage-side surface 531 being concave near the optical axis 590 and animage source-side surface 532 being convex near the optical axis 590,the image-side surface 531 and the image source-side surface 532 areaspheric, and the third lens element 530 is made of plastic material.

The detailed optical data of the fifth embodiment is shown in table 9,and the aspheric surface data is shown in table 10.

TABLE 9 Embodiment 5 f(focal length) = 4.99 mm, Fno = 2.9, FOV = 11.55deg. surface Curvature Radius Thickness Material Index Abbe # Focallength 0 object infinity 700 1 infinity 0.475 2 stop infinity −0.475 3Lens 1 0.950 (ASP) 0.729 plastic 1.636 24 1.738 4 6.244 (ASP) 0.688 5Lens 2 −1.054 (ASP) 0.250 plastic 1.636 24 −0.635 6 0.671 (ASP) 0.592 7Lens 3 −1.931 (ASP) 0.708 plastic 1.636 24 1.620 8 −0.747 (ASP) 0.542 9Image infinity — source plane

TABLE 10 Aspheric Coefficients surface 3 4 5 K: −2.7420E−01 −1.6911E+02−3.4863E+01 A: 1.3875E−02 1.3776E−01 −2.7815E+00 B: 5.2786E−02−2.0290E−01 3.8359E+01 C: −6.5696E−01 2.7933E−01 −6.6769E+02 D:2.9206E+00 4.3081E−01 8.2840E+03 E: −6.0432E+00 −2.8168E+00 −6.4380E+04F: 6.1794E+00 4.1303E+00 2.7203E+05 G −2.5428E+00 −2.1983E+00−4.7200E+05 surface 6 7 8 K: 1.3533E+00 −1.0420E+02 −1.6517E+00 A:2.1378E+00 −1.6499E+00 −6.0543E−01 B: −1.3383E+01 1.4976E+01 1.9897E+00C: −1.5477E+02 −1.4123E+02 −1.2642E+01 D: 9.0302E+03 8.9439E+023.8353E+01 E: −1.4189E+05 −3.4580E+03 −6.1002E+01 F: 9.9128E+057.1314E+03 3.7651E+01 G −2.6000E+06 −5.8773E+03 −7.5000E−01

In the fifth embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the fifth embodiment, so an explanation inthis regard will not be provided again.

Moreover, these parameters can be calculated from Table 9 and Table 10as the following values and satisfy the following conditions:

Embodiment 5 f [mm] 4.99 f12/f3 3.745 Fno 2.9 f/TL 1.423 FOV [deg.]11.55 R1/R2 0.152 f/f12 0.823 R3/R4 −1.571 f/f23 1.197 R5/R6 2.586 f1/f2−2.739 CT1/CT2 2.915 f2/f3 −0.392 CT2/CT3 0.353 f1/f3 1.073 CT1/CT31.030 f1/f23 0.417

In the present three-piece infrared single wavelength projection lenssystem, the lens elements can be made of plastic or glass. If the lenselements are made of plastic, the cost will be effectively reduced. Ifthe lens elements are made of glass, there is more freedom indistributing the refractive power of the three-piece infrared singlewavelength projection lens system. Plastic lens elements can haveaspheric surfaces, which allow more design parameter freedom (thanspherical surfaces), so as to reduce the aberration and the number ofthe lens elements, as well as the total track length of the three-pieceinfrared single wavelength projection lens system.

In the present three-piece infrared single wavelength projection lenssystem, if the image-side or the image source-side surface of the lenselements with refractive power is convex and the location of the convexsurface is not defined, the image-side or the image source-side surfaceof the lens elements near the optical axis is convex. If the image-sideor the image source-side surface of the lens elements is concave and thelocation of the concave surface is not defined, the image-side or theimage source-side surface of the lens elements near the optical axis isconcave.

While we have shown and described various embodiments in accordance withthe present invention, it should be clear to those skilled in the artthat further embodiments may be made without departing from the scope ofthe present invention.

What is claimed is:
 1. A three-piece infrared single wavelengthprojection lens system, in order from an image side to an image sourceside, comprising: a first lens element with a positive refractive power,having an image-side surface being convex near an optical axis, at leastone of the image-side surface and an image source-side surface of thefirst lens element being aspheric; a second lens element with a negativerefractive power, having an image source-side surface being concave nearthe optical axis, at least one of an image-side surface and the imagesource-side surface of the second lens element being aspheric; a thirdlens element with a positive refractive power, having an image-sidesurface being concave near the optical axis and an image source-sidesurface being convex near the optical axis, at least one of theimage-side surface and the image source-side surface of the first lenselement being aspheric; and a stop disposed before the image source-sidesurface of the first lens element or between the image-side surface ofthe first lens element and the image source-side surface of the secondlens element.
 2. The three-piece infrared single wavelength projectionlens system as claimed in claim 1, wherein a focal length of thethree-piece infrared single wavelength projection lens system is f, afocal length of the first lens element and the second lens elementcombined is f12, and they satisfy the relation: 0.6<f/f12<1.6.
 3. Thethree-piece infrared single wavelength projection lens system as claimedin claim 1, wherein a focal length of the three-piece infrared singlewavelength projection lens system is f, a focal length of the secondlens element and the third lens element combined is f23, and theysatisfy the relation: 0.1<f/f23<1.3.
 4. The three-piece infrared singlewavelength projection lens system as claimed in claim 1, wherein a focallength of the first lens element is f1, a focal length of the secondlens element is f2, and they satisfy the relation: −3.0<f1/f2<−1.7. 5.The three-piece infrared single wavelength projection lens system asclaimed in claim 1, wherein a focal length of the second lens element isf2, a focal length of the third lens element is f3, and they satisfy therelation: −0.55<f2/f3<−0.15.
 6. The three-piece infrared singlewavelength projection lens system as claimed in claim 1, wherein a focallength of the first lens element is f1, the focal length of the thirdlens element is f3, and they satisfy the relation: 0.5<f1/f3<1.3.
 7. Thethree-piece infrared single wavelength projection lens system as claimedin claim 1, wherein a focal length of the first lens element is f1, afocal length of the second lens element and the third lens elementcombined is f23, and they satisfy the relation: 0.02<f1/f23<0.46.
 8. Thethree-piece infrared single wavelength projection lens system as claimedin claim 1, wherein a focal length of the first lens element and thesecond lens element combined is f12, a focal length of the third lenselement is f3, and they satisfy the relation: 1.34<f12/f3<4.05.
 9. Thethree-piece infrared single wavelength projection lens system as claimedin claim 1, wherein a radius of curvature of the image-side surface ofthe first lens element is R1, a radius of curvature of the imagesource-side surface of the first lens element is R2, and they satisfythe relation: −3.38<R1/R2<0.45.
 10. The three-piece infrared singlewavelength projection lens system as claimed in claim 1, wherein aradius of curvature of the image-side surface of the second lens elementis R3, a radius of curvature of the image source-side surface of thesecond lens element is R4, and they satisfy the relation:−1.87<R3/R4<6.23.
 11. The three-piece infrared single wavelengthprojection lens system as claimed in claim 1, wherein a radius ofcurvature of the image-side surface of the third lens element is R5, aradius of curvature of the image source-side surface of the third lenselement is R6, and they satisfy the relation: 0.5<R5/R6<3.2.
 12. Thethree-piece infrared single wavelength projection lens system as claimedin claim 1, wherein a central thickness of the first lens element alongthe optical axis is CT1, a central thickness of the second lens elementalong the optical axis is CT2, and they satisfy the relation:0.8<CT1/CT2<3.5.
 13. The three-piece infrared single wavelengthprojection lens system as claimed in claim 1, wherein a centralthickness of the second lens element along the optical axis is CT2, acentral thickness of the third lens element along the optical axis isCT3, and they satisfy the relation: 0.1<CT2/CT3<1.6.
 14. The three-pieceinfrared single wavelength projection lens system as claimed in claim 1,wherein a central thickness of the first lens element along the opticalaxis is CT1, a central thickness of the third lens element along theoptical axis is CT3, and they satisfy the relation: 0.1<CT1/CT3<1.1. 15.The three-piece infrared single wavelength projection lens system asclaimed in claim 1, wherein a focal length of the three-piece infraredsingle wavelength projection lens system is f, a distance from theimage-side surface of the first lens element to an image plane along theoptical axis is TL, and they satisfy the relation: 1.0<f/TL<2.0.
 16. Thethree-piece infrared single wavelength projection lens system as claimedin claim 1, wherein a refractive index of the first lens element is n1,a refractive index of the second lens element is n2, a refractive indexof the third lens element is n3, and they satisfy the relations: n1>1.6,n2>1.6 and n3>1.6.